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Homework Help: Energy and Power problem (change in tempurature)

  1. Jan 17, 2010 #1
    1. The problem statement, all variables and given/known data
    David is travelling in his car (1500 kg) at 72 km/h. He sees a dog on the road and hits the brakes, what is the final temperature of his brake pads if they have a combined mass of 10 kg, a heat capacity of 300 J/kgC and they start at 20 degrees Celsius?


    2. Relevant equations

    Q=mcT
    Change in T=T2-T1

    3. The attempt at a solution

    I am wondering if i have done this right

    Ek=1/2mv^2
    = 1/2*1500kg*20m/s^2
    =300000
    -3.0x10^5 J

    change in temperature =Q/mc
    =3.0x10^5 J/10 kg*300 J/kgC
    =100 degrees C
    100+20=120 degress Celsius

    120 is final temperature of break
    -Is this correct?
     
  2. jcsd
  3. Jan 17, 2010 #2

    PhanthomJay

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    Science Advisor
    Homework Helper
    Gold Member

    Looks good! Some of the kinetic energy may be lost to sound, etc., but essentially, all of the kinetic energy is transformed to heat energy.
     
  4. Jan 17, 2010 #3
    Thank you!
     
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